Re: [PATCH 09/17] hw/vfio/pci-quirks: Fix missing ERRP_GUARD() for error_prepend()

[Cédric Le Goater]

On 2/29/24 15:39, Zhao Liu wrote:

From: Zhao Liu <zhao1....@intel.com>

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.

ERRP_GUARD() could avoid the case when @errp is the pointer of
error_fatal, the user can't see this additional information, because
exit() happens in error_setg earlier than information is added [1].

In hw/vfio/pci-quirks.c, there're 2 functions passing @errp to
error_prepend() without ERRP_GUARD():
- vfio_add_nv_gpudirect_cap()
- vfio_add_vmd_shadow_cap()

Their @errp parameters are so widely sourced that it is necessary to
protect them with ERRP_GUARD().

To avoid the issue like [1] said, add missing ERRP_GUARD() at the
beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
      ("error: New macro ERRP_GUARD()").

Cc: Alex Williamson <alex.william...@redhat.com>
Cc: "Cédric Le Goater" <c...@redhat.com>
Signed-off-by: Zhao Liu <zhao1....@intel.com>

Reviewed-by: Cédric Le Goater <c...@redhat.com>

Thanks,

C.

---
  hw/vfio/pci-quirks.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/hw/vfio/pci-quirks.c b/hw/vfio/pci-quirks.c
index 84b1a7b9485c..496fd1ee86bd 100644
--- a/hw/vfio/pci-quirks.c
+++ b/hw/vfio/pci-quirks.c
@@ -1538,6 +1538,7 @@ static bool is_valid_std_cap_offset(uint8_t pos)

static int vfio_add_nv_gpudirect_cap(VFIOPCIDevice *vdev, Error **errp)

  {
+    ERRP_GUARD();
      PCIDevice *pdev = &vdev->pdev;
      int ret, pos;
      bool c8_conflict = false, d4_conflict = false;
@@ -1630,6 +1631,7 @@ static int vfio_add_nv_gpudirect_cap(VFIOPCIDevice *vdev, 
Error **errp)
  #define VMD_SHADOW_CAP_LEN 24
  static int vfio_add_vmd_shadow_cap(VFIOPCIDevice *vdev, Error **errp)
  {
+    ERRP_GUARD();
      uint8_t membar_phys[16];
      int ret, pos = 0xE8;